Imagine there's a (regular) cold war going on as Romulans keep trying to Blow up Enterprise and blame it on the Vulcans because no one knows that Vulcans and Romulans are identical.
Political squabbles between Earth and the Lunal, Martian and Jupitarian Colonies, and just because they haven't left earth, that still doesn't disqualify the introduction of the temporal cold war and the Suliban come to Earth... And just because Enterprise is half constructed, you don't think anything called "Starfleet" only had one ship and before 2151 had no ships? Sure they needed warp 5 to explore the "sector" but as long as the bad guys kept coming to them, they had plenty of firepower enough to keep their flag planted.
When mirror Archer got hold of the Defiant, short on a change of clothes, his crew began looting the ship for fresh underwear and other accoutrements, so maybe Future Archer looks like he's dressed as a Romulan, because he's driving a stolen Romulan Warbird and he's dressed as a Romulan?
In the Napoleonic war pulp novels "Sharpe", Richard Sharpe used to get into a lot of trouble with the proper officers because half his kit was French. So what if the French were all evil and inbred, they really knew how to stitch up a pair of jodhpurs.
I imagine Starfleet briefs are cotton, and Romulans wear silk boxers.
Not much of a choice really.
Klingons obviously have as yet not invented underwear by the 22nd century.